This project is designed to investigate the spatial distribution and functional properties of cortical neuron "colonies" in the primate motor cortex that project to the spinal cord and are associated with individual muscles or closely related groups of muscles, as well as the activity of neurons in such colonies during defined voluntary motor behaviors. Intracortical microstimulation (ICMS) is used to map regions that produce excitation or inhibition of particular muscles or muscle groups, and the resultant cortical maps are compared with those for synergist or antagonist muscle groups. To obtain an accurate map, ICMS is done while the animal is performing a task and EMG activity is monitored. Cortical cell discharge patterns during normal movements are evaluated with respect to the excitation or inhibition of muscle activity that is produced by ICMS, and also in terms of EMG patterns. Spinal cord location of motoneurons innervating selected forelimb muscles are studied using retrograde tracing methods. Histochemical studies of muscle fiber types are also performed.